a) Field of the Invention
The present invention relates to method and apparatus for estimating a sideslip angle of an automotive vehicle.
b) Description of the Related Art
A previously proposed method for estimating a sideslip angle of an automotive vehicle is exemplified by a Japanese document volume No. 964 for an academic lecture meeting of a Society of Automotive Engineers published on Oct. in 1996.
The previously proposed estimating method for the automotive vehicle generally includes two steps of a road surface circumstance determining step; and a sideslip angle estimating step using a vehicular bicycle model.
In the side slip angle estimating step, the side slip angle estimating equation is calculated using a motion equation in the vehicular bicycle model (mathematical model) on the basis of a steering angle, an acceleration, a yaw rate, and a vehicle speed.
At this time, a cornering power Cf on two front road wheel's tires and a cornering power Cr on two rear road wheel's tires are corrected after the determination of a road surface circumstance (for example, a (dry road surface, a wet road surface, a snow road surface, or an icy road surface) since these cornering powers are largely varied according to the road surface circumstance.
That is to say, the estimated value (.beta. ') of the side slip angle (.beta.) in the previously proposed sideslip angle is calculated as follows: EQU .beta. '={MV(d.beta./dt+d.theta./dt)+(CfLf-CrLr)d.theta./dt/V-Cf.delta.f-Cf.beta. f-Cr.beta.r+F+R}/Cf+Cr).
In details, in the road surface circumstance determining step, an estimated value of the yaw rate and the detected value of the yaw rate are stored in time series data. The estimated value of the yaw rate is calculated as follows: EQU d.theta. /dt=1/(1+AV.sup.2).times.(V/L).times..delta.f,
wherein A denotesa stability factor, V denotes the vehicle speed, .delta.f denotes the steering angular displacement (steered angle), and L=Lf+Lr and denotes a wheel base.
Then, a trajectory between the estimated value of the yaw rate and the detected value of the yaw rate after a constant period of time from the time at which the time series data are stored is plotted. At this time, a phase deviation of the estimated value of the yaw rate with respect to the detected value of the yaw rate is determined according to the time series data. The plotted trajectory is used to determine the road surface circumstance.